Yo, don't draw every day.
It's an epic bold statement that sounds good.
But easily leads to RSI in the hands, a decline in mental health, and lacks life balance.
IMO a strong and steady pace *does* need to be every day (with the exact *amount* per day being more flexible).
15min a day is IMO a good way to start out, to develop the drawing habit, and I would say it is in no way excessive or unhealthy[1].
I'd suggest 15min as a minimum amount because it takes a certain amount of focused effort before your feelings start getting onboard with the idea of 'working on this drawing task for no less than 15min'. Sessions shorter than this are IMO not effective at reinforcing that habit of focus, which is absolutely needed to learn effectively. [2]
There are also natural opportunities to draw in some cases (for example, on buses, or when making notes). Taking this 'lifestyle' approach - don't just give it a timeslot, but find ways to fit it into the context of other tasks - IMO is necessary to ensure consistent progress. This eventually makes the plan of 'draw something every day' quite easy to achieve.
[1] re: RSI, As a side issue: another thing a newbie should be aware of that can have a big impact, both on drawing quality and RSI:
Don't press so hard. Using the minimum possible pressure wins on three fronts: less pencil wear, less body wear (ie. protecting yourself from RSI), smoother lines. People often cite control as a reason why they press hard, but the same level of control can be achieved by training your muscle control instead (particularly, working to draw mainly via shoulder motion rather than elbow or wrist motion).
[2] Learnt this from Nicolaides' "Natural Way to Draw", FWIW. I also recommend this book on the basis of Nicolaides' ability to teach techniques that *make you think about the subject*, rather than providing a neat way to reproduce the surface appearance.